YouTube is terrible. Why would anyone buy a professionally produced DVD if they can just get stuff for free from YouTube? Eventually someone will rip the DVD content and post it to YouTube anyway.

DVDs are a great way for a dojo to make some extra cash.

Besides the quality of the video (not the content but the picture size, resolution , color clarity, etc) is typically so poor on YouTube it subtracts a great deal from the content.

For the teachers who really matter, I think the serious student will spend the cash to get the DVD. For instance, clips from Endo's DVDs are on Youtube, but I have bought all his DVDs anyway. Now waiting for the next one.